Coupled Multi-Physics Modeling of Micro-Machined Electro-Thermo-Mechanical Actuator

Electro-thermal actuation mechanism continues to attract attention of MEMS designers as a reliable method of delivering high displacements and high actuation forces [1]. The main purpose of this work is to conduct a coupled multi-physics FEA of a micro-machined electro-thermomechanical actuator (μETMA) in order to determine a nature of a common failure mode, suggest a better fabrication process and compute performance characteristics, such as actuation current, working temperature, actuation force and displacement, characteristic response time, etc. Two designs of μETMA have been considered so far: design for PolyMUMPs and design for MetalMUMPs processes [2]. Comprehensive coupled multi-physics modeling of the device should includ the following phenomena: initial relaxation of the structure due to residual stresses inherent to micro-fabrication methods, computation of electric current through the structure with semiconductor and metallic types of conductivity, Joule’s heating, radiation and natural convection, thermal expansion, modal analysis, air-structure interaction, etc. Current paper presents only several analyses accomplished so far. It has been determined that common mode failure observed with polysilicon devices is caused by run off temperature behavior due to exponential temperature dependence of the conductivity.

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